Butter the sides and base of the muffin tins. Preheat the oven to moderately hot (190Â°C). Sift the ingredients into a mixing bowl. Whisk the egg whites with a fork until broken and slightly frothy and add to mixture. Stir in the bananas, oil, yoghurt and nuts and mix lightly until just combined. Spoon into the tins and bake for about 20 minutes or until golden and firm to the touch on top. Transfer to a wire cake rack and eat!